1. Field of the Invention
The present invention relates to a vibration type actuator.
2. Related Background Art
A vibration type actuator apparatus or a vibration type (vibration wave) motor, which generates surface acoustic wave vibrations, using an electro-mechanical energy conversion element such as a piezoelectric element, attached to a vibration member, on the surface of the vibration member, and converts the vibration energy of the vibration member into a continuous mechanical motion, has already been put into practical applications such as a driving motor for an optical equipment such as a camera by the present applicant.
A bar-shape vibration type (vibration wave) motor developed by the present applicant and built in an optical equipment will be described below as prior art associated with the present invention.
FIGS. 9 and 10 respectively show the mechanical structure and the electrical arrangement of the bar-shape vibration wave motor. Referring to FIG. 9, a vibration member 101 of the motor is formed by sandwiching groups of annular piezoelectric elements (groups of electro-mechanical energy conversion elements) at the middle portion of a vibration member main body also consisting of a thick, metal cylindrical member. When alternating voltages with different phases are applied to the groups of piezoelectric elements, a local elliptic motion is generated on the distal end face of the vibration member 101. The piezoelectric elements sandwiched in the vibration member main body include groups of A and B phase piezoelectric elements (groups of electro-mechanical energy conversion elements for driving) to which first and second alternating voltages are applied to generate the local elliptic motion on the distal end face of the vibration member 101, and a vibration detection piezoelectric element S (a mechano-electro energy conversion element for detection) for detecting the vibrating state of the vibration member 101.
A rotary member (rotor) 102 serving as a movable member is in press-contact with the distal end face of the vibration member 101, and is rotated by surface acoustic wave vibrations generated on the distal end face of the vibration member. An output gear 103 is coupled to the rotor 102. Note that + and - in the piezoelectric elements in FIG. 9 indicate the polarities of the polarization process.
Note that the operation principle of this vibration wave motor is disclosed in, e.g., Japanese Laid-Open Patent Application No. 3-289375 and the like, and a detailed description thereof will be omitted.
A piezoelectric element portion of the vibration member portion 101 is constituted by A phase piezoelectric elements a1 and a2 and B phase piezoelectric elements b1 and b2, which are used for driving, and a vibration detection piezoelectric element S1. The piezoelectric elements are driven by applying an A phase application cyclic voltage to a metal plate (A-d) sandwiched between the A phase piezoelectric elements a1 and a2, and a B phase application cyclic voltage (which has a phase different from that of the A phase application cyclic voltage signal) to a metal plate (B-d) sandwiched between the B phase piezoelectric elements b1 and b2. The outer surfaces of the A phase piezoelectric elements a1 and a2 and the B phase piezoelectric elements b1 and b2 are set at the GND potential by means of metal plates (GND-d). At this time, metal plates present between the elements a2 and b1 and between the elements b2 and S1 are set at the GND potential since they are in contact with a metal bolt (not shown) extending through the vibration member 101. Likewise, one surface (the B phase side in FIG. 9) of the vibration detection piezoelectric element S1 is set at the GND potential, and a signal is picked up from the opposite surface. The signal pickup surface side of the vibration detection piezoelectric element S1 contacts a metal block, which is insulated from the GND potential by an insulation sheet. Hence, the vibration detection piezoelectric element S1 can generate an output voltage corresponding to the detected vibrations. A resonance frequency and the like are calculated on the basis of the magnitude of the output voltage, the phase differences between the output voltage and driving voltages, and the like.
FIG. 10 shows a driving circuit when such vibration wave motor is used.
An oscillator 2 generates an alternating voltage, and is connected to a 90.degree. phase shifter 3. Switching circuits 4 and 5 switch the power supply voltage using alternating voltages supplied from the oscillator 2 and the phase shifter 3. Booster coils 6 and 7 amplify pulse voltages switched by the switching circuits 4 and 5. A phase difference detector 10 detects a signal phase difference .phi. between a driving electrode A-d and a vibration detection electrode S-d.
A control microcomputer 11 serves as control means. The microcomputer 11 sets a driving frequency, and the vibration wave motor is driven based on the set frequency.
A position detector (e.g., an encoder) 8 detects the position of the motor. The control microcomputer 11 obtains position information on the basis of the signal output from the position detector 8, and controls the motor to stop at an appropriate position. With this control, the motor can stop at a predetermined position.
As can be seen from the above-mentioned prior art, the vibration type actuator apparatus or the vibration wave motor requires a position sensor such as an encoder when the rotational speed upon driving the movable member which is in press-contact with the upper portion of the vibration member by friction is to be checked or when the movable member is to be stopped at a specific position, resulting in high cost and an extra space for mounting the position sensor.